IMPULSE OF THE HEART. 133 



a slight shock or impulse against the walls of the chest. 

 This impulse is most evident in the space between the fifth 

 and sixth ribs, between one and two inches to the left of 

 the sternum. The force of the impulse, and the extent to 

 which it may be perceived beyond this point, vary con- 

 siderably in different individuals, and in the same indi- 

 viduals under different circumstances. It is felt more 

 distinctly, and over a larger extent of surface, in emaciated 

 than in fat and robust persons, and more during a forced 

 expiration than in a deep inspiration ; for, in the one case, 

 the intervention of a thick layer of fat or muscle between 

 the heart and the surface of the chest, and in the other the 

 inflation of the portion of lung which overlaps the heart, 

 prevents the impulse from being fully transmitted to the 

 surface. An excited action of the heart, and especially a 

 hypertrophied condition of the ventricles, will increase the 

 impulse, while a depressed condition, or an atrophied state 

 of the ventricular walls, will diminish it. 



The impulse of the heart is probably the result, in part, 

 of a tilting forwards of the apex, so that it is made to 

 strike against the walls of the chest. This tilting move- 

 ment is thought to be effected by the contraction of the 

 spiral muscular fibres of the ventricles, and especially of 

 certain of these fibres which, according to Dr. Beid, arise 

 from the base of the ventricular septum, pass downwards 

 and forwards, forming part of the septum, then emerge 

 and curve spirally around the apex and adjacent portion 

 of the heart. The whole extent of the movement thus 

 produced is, however, but slight. The condition, which, 

 no doubt, contributes most to the occurrence and character 

 of the impulse of the heart, is its change of shape ; for, 

 during the contraction of the ventricles, and the consequent 

 approximation of the base towards the apex, the heart 

 becomes more globular, and bulges so much, that a distinct 

 impulse is felt when the finger is placed over the bulging 

 portion, either at the front of the chest, or under the 



